Generally, paint coating systems in use for painting vehicle bodies and the like are largely constituted by a robot device with an articulated arm, and a coater unit mounted on a distal end of the robot arm of the robot device and provided with an atomizing head for spraying atomized paint particles.
Among paint coating systems of this sort, there is a system providing a plural number of atomizing heads which can be replaceably attached to a common body which is mounted on a distal end of a robot arm of the robot device (see, for example, Patent Literature 1: Japanese Patent Laid-Open No. 2001-79463). In another paint coating system, paint cartridges filled with paint, which is supplied for atomizing heads, are interchangeably attached to the common body (see, for example, Patent Literature 2: Japanese Patent Laid-Open No. 2000-176333).
When replacing an atomizing head on a common body of a coater unit, a robot arm of the robot device operates to attach an atomizing head on the common body to an atomizing head gripper of an atomizing head changing and washing device. In this state, the common body is lifted up by the robot device to detach the used atomizing head from the common body. On the other hand, after detachment of the used atomizing head, the common body is transferred by a robot device to an atomizing head changing position for replacement by a washed atomizing head which is held on an atomizing head gripper.
Further, when replacing paint cartridges on a common body of a coater unit, the coater unit is transferred to and located in a predetermined cartridge changing position by a robot arm of a robot device, and the action of the robot arm is stopped there. In this state, a used paint cartridge is detached from the common body by a cartridge changer, which is moved upward after gripping the used paint cartridge by a cartridge gripper. In the meantime, the robot device is stopped at the predetermined cartridge changing position while another paint cartridge, which has been replenished with paint, is mounted on the common body from above by the cartridge changer.
In this connection, in the case of the paint coating system of Patent Literature 1, an atomizing head is replaced by moving a coater unit up and down relative to an atomizing head gripper which is held in a fixed state.
On the other hand, in the case of the paint coating system of Patent Literature 2, a robot arm of a robot device is stopped at a predetermined cartridge changing position to locate and set a coater unit in that position while a paint cartridge is replaced by a cartridge changer.
However, in the case of a robot device which is in use for paint coating operations, with regard to the repeated positioning accuracy in motion control such as moving, stopping, posture and the like of a coater unit which is mounted on a distal end of a robot arm, there is inevitably an error of several millimeters. Therefore, even if the coater unit is moved to a predetermined position for changing an atomizing head or a paint cartridge in response to the same control command after finishing a certain coating operation by the robot device, actually it is often the case that the coater unit is located in a position which is somewhat deviated from the predetermined changing position. Therefore, if the changing operation is carried out depending upon the accuracy of motion control on the part of the robot device alone, this deviation from the predetermined changing position may result in exertion of a forcible load between a common body and the atomizing head or the paint cartridge, shortening the service life of the coater unit by repeated abrasive and damaging contact.
Besides, a robot device is required to be operative with an extremely high degree of accuracy in locating a coater unit in a predetermined changing position at the time of changing a paint cartridge, and, in order to meet this requirement, needs to be installed with high dimensional accuracy despite a considerable increase in cost.